1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, and a digital multifunction product of an electrophotographic system, and more particularly, to an image forming apparatus including a plurality of heating units in a fixing device that fixes a toner image on a recording medium and a method of controlling the image forming apparatus.
2. Description of the Related Art
In recent years, there is an increasing demand for high image formation speed in image forming apparatuses. To realize the high image formation speed, the image forming apparatuses are increased in size and power consumption thereof also increases.
In particular, large electric power is necessary in an image forming apparatus that uses a fixing device of a heat roller system for pressing and heating a member to be heated such as paper or film having a toner image formed thereon.
In a high-speed image forming apparatus, a plurality of heaters as heating means are necessary to reduce warm-up time of a fixing device. When the heaters of the fixing device are turned on and off, fluctuation in a power supply voltage tends to be caused by current consumption and the like of the heaters. This may cause flicker, harmonic distortion, terminal noise, and the like in other electronic apparatuses that use the same power supply. Therefore, it is necessary to take measures for suppressing the fluctuation in a power supply voltage.
As such measures, for example, Japanese Patent Application Laid-open No. 2003-217793 discloses a method of, when electric power is supplied to a plurality of heaters in a fixing device, rather than simultaneously turning the heaters on, turning the heaters on at delayed timing while soft-starting the heaters individually.
However, in such conventional power supply control method, when a plurality of heaters in a fixing device are driven, there must be a period in which all heaters are turned on because the turn-on start timing is simply delayed, and an effect for reducing fluctuation in a power supply voltage is not enough, which may cause ripple, flicker, and the like in other electronic apparatuses that use the same power supply.